The Materials Core provides samples of well-characterized Superfund-related particles and surrogates designed to test specific research hypotheses for study by the 6 research projects. The Core was constructed to assist in the study of the health and environmental effects of environmentally persistent free radicals (EPFRs) associated with transition metal-containing particulate matter (PM). Our researchers have discovered EPFRs are formed by chemisorption of aromatic chlorinated benzenes, chlorinated phenols, and other types of phenols to metal oxides, followed by electron transfer that reduces the metal and forms the EPFR. These EPFRs can persist in the environment and are biologically active. At high concentrations in combustion and thermal processing systems, they also self-react to form new pollutants such as polychlorinated dibenzo-p-dioxins and dibenzofurans. Because fine particles and ultrafine particles have high surface-to-volume ratios and increased reactivity due to unsatisfied valences, they may be particularly prone to EPFR formation. The Core has developed facilities and techniques to synthesize: i) fine and ultrafine particles of silica coated with a monolayer of transition metals such as copper oxide and iron oxide;ii) fine and ultrafine silica particles containing size-controlled nanodomains of the same transition metals;iii) ultrafine particles of pure copper and iron oxides;iv) any of these particles with associated environmentally persistent free radicals (EPFRs);and v) appropriate control samples. The Core has also established the capabilities to characterize field samples from contaminated Superfund soils and particulate emissions of devices for thermal treatment of hazardous substances for EPFRs using electron paramagnetic resonance (EPR) spectroscopy and molecular precursors using GC-MS and other standard laboratory techniques. The Core has developed systematic approaches for receiving sample requests, establishing chain of custody, and storing particles under vacuum where they will not degrade prior to use. The Core Director has a record of successful collaborations with each of the Project Leaders over the past 5 years, leading to multiple publications.